Apparatus for degolding or tinning conductive portions of a microelectronic device

ABSTRACT

The apparatus is used for processing a microelectronic device having a face with electrically conductive elements arranged thereon. The apparatus comprises a vessel for containing a solder melt, a bowl for drawing molten solder from the vessel, a device holder for holding the microelectronic device with said face directed downwardly, and drive means for moving the bowl and the device holder vertically with respect to each other, thereby allowing said conductive elements to be immersed in molten solder drawn by the bowl. The bowl has an upper rim with an upwardly directed acute angled edge extending therealong.

This is a division of application Ser. No. 07/980,160 filed Nov. 23,1992, now U.S. Pat. No. 5,288,009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for processing amicroelectronic device and in particular to an apparatus for degoldingor applying tin solder on electrically conductive elements arranged on aface of the device.

2. Description of the Related Art

In solder processing of electronic parts it is known that pre-tinningbefore soldering is necessary and that fresh pre-tinning is preferableto the electro-deposition techniques.

In the processing of microelectronic devices such as chip carriers, itis known to remove gold and/or to tin the conductive elements on adevice face by dipping said face in a solder melt. Several processes areknown for removing excess of tin: shocks or soaking the device in oil,or spinning the device about an axis perpendicular to said face.

The solder melt is at medium temperature recommended by the process andstandards (230° C. as an example), and the solder material which iswithdrawn by the device cools down rapidly after the separation.Accordingly, in order to achieve a solder deposit of regular thicknesson the conductive elements, and to efficiently eliminate the moltensolder remaining on the non-conductive portions of the device, it isdesired to start the spinning operation as soon as possible after theconductive elements are separated from the melt, i.e. after the meniscusbetween the device face and the melt breaks. However, the level of thesolder melt is not known accurately when a series of devices areprocessed successively because an amount of solder is withdrawn from themelt by each processed device, so that it is difficult to determine whenthe spinning operation should be started. It is possible to attach alevel sensor to the device holder for detecting the melt level andcontrolling the spinning operation in response thereto. However theoperation of such sensor implies specific signal transmission andprocessing means and delays the beginning of the spinning step.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to improve theabove-discussed apparatus in order to achieve an accurate andreproducible melt level, so that appropriate control permits thespinning operation to start as early as desired after the separation.

According to the invention, there is provided an apparatus forprocessing a microelectronic device having a face with electricallyconductive elements arranged thereon, comprising a vessel for containinga solder melt, a bowl having a horizontal upper rim for drawing moltensolder from the vessel, a device holder for holding the microelectronicdevice with said face directed downwardly, and drive means for movingthe bowl and the device holder vertically with respect to each other,thereby allowing said conductive elements to be immersed in moltensolder drawn by the bowl. The upper rim of the bowl has an upwardlydirected acute angled edge extending therealong.

Initially, the bowl is completely immersed in the melt. The surface ofthe liquid is cleaned by sweeping the lighter surface oxides aside. Thenthe bowl is lifted to a position where at least the upper rim is locatedabove the melt level. The edge along the upper rim promotes the rapidformation of a meniscus between the molten solder and the bowl wall. Inaddition, it ensures a clean, accurate and reproducible level of moltensolder in the bowl. The device face can be immersed in the solder drawnby the bowl, and then separated therefrom. The instant of separation isvery well determined due to the accuracy of the solder level.Immediately after separation, the device is spun with a profile ofangular acceleration, maximum angular velocity and angular decelerationso selected as to leave the desired solder thickness on the conductiveelements. The machine allows the tinning process to be undertaken in gasmedia (e.g. dry Nitrogen is frequently used).

Other objects, features and advantages of the present invention willbecome apparent from the following description of a preferred andnon-limitative embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a processing installation which incorporates anapparatus according to the invention.

FIG. 2 is a sectional view of the installation of FIG. 1, according tothe plane denoted as II--II.

FIG. 3 is an elevation view of a device holder of this apparatus.

FIGS. 4-6 are schematic views illustrating the immersion of the devicein molten solder.

FIG. 7 is a view similar to FIG. 5 in the case of another type ofmicroelectronic device.

FIG. 8 is a timing diagram which illustrates a spinning stepaccomplished by the apparatus according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The installation shown in FIG. 1 is used for applying solder onconductive elements of a microelectronic device. The installationcomprises a plurality of stations which may e.g. be disposed in acarousel configuration, i.e. a preheating and loading station S1, adegolding station S2, a tinning station S3, and a cooling and unloadingstation S4. It will be apparent to those skilled in the art that theinstallation may comprise other known stations such as a fluxingstation.

The installation comprises a device holder 1 for holding themicroelectronic device 2 and moving it from station to station. Thedevice 2 has a face 3 with conductive elements 4, e.g. contact pins,arranged thereon. As best shown in FIG. 3, the device holder 1 isadapted to hold the device 2 with the face 3 directed downwardly.Various holding modes are suitable, for instance using suction means. Inthis case, the holder 1 is a nozzle so configured as to match the deviceshape, thereby ensuring an accurate positioning of the device.Alternative holding modes are by means of adhesives, magnets orelectromagnets.

The device holder is mounted on a bracket 6 which is secured to ahorizontal support rotatably mounted about the carousel axis A (FIG. 1and 2). An actuator 5 is connected to support 7 for moving it between anupper position shown in the left-hand portion of FIG. 2 and a lowerposition shown in the right-hand portion of FIG. 2. As shown in FIG. 3,a first motor 8 is attached to bracket 6 for moving the device holder 1along a substantially vertical axis B, and a second motor 9 is provided,together with an appropriate transmission 9a, 9b, for rotating thedevice holder 1 about axis B at a controllable velocity.

The tinning station shown in FIG. 1 and 2 comprises a vessel 12 forcontaining a Sn--Pb solder melt 13, and a bowl 14 which is slidablymounted along a vertical direction. The bowl 14 is attached to a bracket16 via an arm 17. The bracket 16 is guided along a vertical rod 18, andconnected to an actuator 19 for obtaining the vertical displacement ofbowl 14. The vessel 12 is associated with heating means (not shown) forheating the solder material to a selectable temperature higher than itsmelting point.

The upper rim of bowl 14 extends in a horizontal plane. As shown inFIGS. 4-7, this rim has an upwardly directed edge 21 extendingtherealong. The edge 21 forms an cute angle of from 15° to 60°. In theillustrative embodiment, this angle is about 45°. The upwardly directededge 21 is formed at the intersection of the inner surface 22 of thebowl and a tapering surface 23 of the bowl which extends downwardlybetween said edge 21 and the outer surface 24 of the bowl.

In operation, the device holder 1 is first brought above the loadingstation S1 in order to grip the microelectronic device which haspreviously been preheated. Station S1 comprises a horizontal rotatingsupport 31 for supporting devices to be processed. The device 2 is firstheated by a radiant element 32, then transferred at the loading place byrotating support 31. There, a vertically sliding push rod 33 gentlylifts the device 2 into contact with the device holder 1. Adepressurization of about 150 mbar is then applied to the latter forfirmly holding the device.

Then the support 7 is rotated to bring the device at the degoldingstation S2 where it is prepared for the tinning step. Thereafter, thesupport 7 is further rotated to bring the device above vessel 12 at thetinning station S3, and lowered by actuator 5 to bring the device closerto the solder melt, as shown in the right-hand portion of FIG. 2.

At this moment, bowl 14 is lifted via actuator 19 from a position whereit is completely immersed in the solder melt 13 contained in vessel 12,so that at least the upper rim of bowl 14 emerges from the melt.Accordingly, bowl 14 draws an amount of molten solder from vessel 12.The tapered shape of the upper rim of bowl 14 ensures a rapid formationof the meniscus 26 (FIGS. 4-7), and an accurate positioning of thesolder level in bowl 14.

The conductive elements 4 of device 2 are immersed into the moltensolder drawn by bowl 14. The immersion is performed by moving bowl 14and device holder 1 vertically with respect to each other via drivemeans which include either motor 8 for further lowering the deviceholder or actuator 19 for lifting the bowl, or both. Once the moltensolder has spread over the conductive elements 4 (FIG. 4), the deviceholder 1 is lifted (and/or the bowl is lowered; see FIG. 5) up to aposition where the conductive elements 4 are separated from the moltensolder (FIG. 6). As soon as the latter position is reached, motor 9 isenergized to cause device 1 to spin about axis B. The rotationalvelocity profile, i.e. the values of the angular acceleration, maximumangular velocity and angular deceleration, is so adjusted as to obtainthe desired solder thickness on elements 4 and eliminate the undesiredsolder on non-conductive portions of the device. Such a profile isillustrated in FIG. 8. The acceleration value (i.e. the slope of thecurve in the acceleration phase), the maximum velocity V_(max), theduration D of the spinning at V_(max), and the deceleration value (i.e.the slope of the curve in the deceleration phase) are selected by theoperator depending on the nature of the conductive elements, thecharacteristics of the solder (composition, temperature . . . ), thedesired solder thickness . . . . As shown in FIG. 1, the installationcomprises a keyboard 36 for entering these parameters and a computer 37to derive the rotational velocity profile therefrom and to control motor9 accordingly. Typical values of the maximum angular velocity V_(max)are between 1 000 and 16 000 rpm, the angular acceleration anddeceleration being from 1 to 300 rounds per square second.

The relative positions of device holder 1 and bowl 14 when the device isseparated from the molten solder are well determined owing to theaccurate positioning of the solder level in bowl 14 which results fromthe shape of its upper rim. Accordingly, appropriate control of motors8, 9 and actuator 19 makes it possible to start the spinning operationas soon as desired after the separation without requiring a speciallevel sensor and the associated signal processing.

Subsequently, the support 7 is further rotated to bring the device atthe cooling and unloading station S4 where it becomes available forfurther processing.

FIG. 7 is a view similar to FIG. 5 in the case where the conductiveelements of the device are metallized pads 4' instead of contact pins 4.In this case, the separation of the conductive elements from the moltensolder (i.e. the break of the meniscus 27 between the solder surface andthe lower face of the device) may occur when the device holder 1 is at adifferent height with respect to the bowl 14. Accordingly, it will beuseful to consider the type of microelectronic device to be processedwhen determining the timing of the spinning operation.

As shown in FIG. 2, the tinning station S3 also includes a horizontalblade scraper 28 which is fixed on a rotatable support 29. When thesupport 29 is rotated about a vertical axis C, the blade scraper 28slides along the surface of the solder melt 13 contained in vessel 12.This sweeps a top layer of the solder melt 13 away from a surface regionlocated above bowl 14 when the latter is completely immersed in the melt13. This sweeping movement is performed before bowl 14 is lifted byactuator 19, in order to remove tin oxide which may otherwise be drawnby the bowl together with the underlying solder.

The degolding station S2 may be used, if necessary, for removing a goldfilm which is provided on the conductive elements of somemicroelectronic devices for protective purposes. In such circumstances,it is desired to remove the gold film before the tinning step becausegold and tin are known to form a compound which is detrimental to thequality of subsequent solderings. The "degolding" step may be effectedbefore the tinning step by means of station S2 which is identical to thetinning station S3. The device is dipped into a solder melt, separatedtherefrom and then spun. The spinning step is similar, with a differentchoice of angular acceleration, rotating velocity, duration and angulardeceleration, in order to virtually eliminate the solder containingtraces of gold. The next station is the tinning station S3 where thedevice is processed as described hereinbefore.

As shown in the top view of FIG. 1, the support 7 preferably carries aplurality of brackets 6 and device holders, whereby the processing ratecan be enhanced. In the exemplary embodiment, four brackets 6 areprovided on the carousel support 7 (one of which is not shown in FIG. 1for exposing vessel 12 and bowl 14 at the tinning station S3), atregular intervals so that the four device holders can staysimultaneously at a respective station.

The invention has been disclosed with reference to a preferredembodiment. However, it will be readily apparent for those skilled inthe related art that many alternative features may be contemplatedwithout departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus for processing a microelectronicdevice having a face with electrically conductive elements arrangedthereon, comprising a vessel for containing a solder melt, a bowl fordrawing molten solder from the vessel, a device holder for holding themicroelectronic device with said face directed downwardly, and drivemeans for moving the bowl and the device holder vertically with respectto each other, thereby allowing said conductive elements to be immersedin molten solder drawn by the bowl, wherein the bowl has an upper rimwhich extends in a horizontal plane, said upper rim being formed by anupwardly directed edge extending therealong, said upwardly directed edgeforming an acute angle of from 15° to 60°.
 2. The apparatus of claim 1,further comprising a blade scraper capable of sliding along the surfaceof the solder melt contained in the vessel for moving a top layer ofsaid molten solder away from a surface region located above the bowlwhen the bowl is completely immersed in the solder melt contained in thevessel.
 3. The apparatus of claim 1, further comprising means forcausing the device holder to spin about a substantially vertical axiswith a first phase of submitting the device holder to a selected angularacceleration, a second phase, having a selected duration, of spinningthe device holder at a selected maximum rotational velocity, and a thirdphase of submitting the device holder to a selected angulardeceleration.
 4. The apparatus of claim 3, wherein said maximumrotational velocity is from 1 000 to 16 000 rpm.
 5. The apparatus ofclaim 3, wherein said angular acceleration and deceleration are from 1to 300 rounds per square second.
 6. Apparatus according to claim 1wherein said upwardly directed edge comprises a surface taperingdownwardly from said edge to a surface of said bowl.
 7. Apparatusaccording to claim 6 wherein said surface of said bowl is the outersurface of said bowl.
 8. Apparatus according to claim 7 wherein saidedge is formed at the intersection of the inner surface of said bowl andsaid downwardly tapering surface.
 9. An apparatus for processing amicroelectronic device having a face with electrically conductiveelements arranged thereon, comprising a vessel for containing a soldermelt, a bowl for drawing molten solder from the vessel, a device holderfor holding the microelectronic device with said face directeddownwardly, and drive means for moving the bowl and the device holdervertically with respect to each other, thereby allowing said conductiveelements to be immersed in molten solder drawn by the bowl, wherein thebowl has an upper rim which extends in a horizontal plane, said upperrim being formed by an upwardly directed edge extending therealong, saidupwardly directed edge comprising a surface tapering downwardly fromsaid edge to a surface of said bowl.
 10. Apparatus according to claim 9wherein said surface of said bowl is the outer surface of said bowl. 11.Apparatus according to claim 10 wherein said edge is formed by at theintersection of the inner surface of said bowl and said downwardlytapering surface.
 12. The apparatus of claim 9, further comprising ablade scraper capable of sliding along the surface of the solder meltcontained in the vessel for moving a top layer of said molten solderaway from a surface region located above the bowl when the bowl iscompletely immersed in the solder melt contained in the vessel.
 13. Theapparatus of claim 9, further comprising means for causing the deviceholder to spin about a substantially vertical axis with a first phase ofsubmitting the device holder to a selected angular acceleration, asecond phase, having a selected duration, of spinning the device holderat a selected maximum rotational velocity, and a third phase ofsubmitting the device holder to a selected angular deceleration.
 14. Theapparatus of claim 13, wherein said maximum rotational velocity is from1,000 to 16,000 rpm.
 15. The apparatus of claim 13, wherein said angularacceleration and deceleration are from 1 to 300 revolutions per squaresecond.
 16. An apparatus for processing a microelectronic device havinga face with electrically conductive elements arranged thereon,comprising a vessel for containing a solder melt, a bowl for drawingmolten solder from the vessel, a device holder for holding themicroelectronic device with said face directed downwardly, drive meansfor moving the bowl and the device holder vertically with respect toeach other, thereby allowing said conductive elements to be immersed inmolten solder drawn by the bowl, and means for causing the device holderto spin about a substantially vertical axis with a first phase ofsubmitting the device holder to a selected angular acceleration, asecond phase, having a selected duration, of spinning the device holderat a selected maximum rotational velocity, and a third phase ofsubmitting the device holder to a selected angular deceleration, whereinthe bowl has an upper rim which extends in a horizontal plane, saidupper rim being formed by an upwardly directed edge extendingtherealong.
 17. The apparatus of claim 16, further comprising a bladescraper capable of sliding along the surface of the solder meltcontained in the vessel for moving a top layer of said molten solderaway from a surface region located above the bowl when the bowl iscompletely immersed in the solder melt contained in the vessel.
 18. Theapparatus of claim 16, wherein said maximum rotational velocity is from1,000 to 16,000 rpm.
 19. The apparatus of claim 16, wherein said angularacceleration and deceleration are from 1 to 300 revolutions per squaresecond.